Proteins regulating cap-dependent translation are downregulated during total knee arthroplasty

Abstract

Total knee arthroplasty (TKA) utilizes a tourniquet to reduce blood loss, maintain a clear surgical “bloodless” field, and to ensure proper bone-implant cementing. In 2007, over 600,000 TKAs were performed in the United States, and this number is projected to increase to 3.48 million procedures performed annually by 2030. The acute effects of tourniquet-induced ischemia-reperfusion (I/R) on human skeletal muscle cells are poorly understood and require critical investigation, as muscle atrophy following this surgery is rapid and represents the most significant clinical barrier to long-term normalization of physical function. To determine the acute effects of I/R on skeletal muscle cells, biopsies were obtained at baseline, maximal ischemia (prior to tourniquet release), and reperfusion (following tourniquet release). Quadriceps volume was determined before and 2 wk post-TKA by MRI. We measured a 36% decrease in phosphorylation of Akt Ser473during ischemia and 37% during reperfusion ( P < 0.05). 4E-BP1 Thr37/46phosphorylation decreased 29% during ischemia and 22% during reperfusion ( P < 0.05). eEF2 Thr56phosphorylation increased 25% during ischemia and 43% during reperfusion ( P < 0.05). Quadriceps volume decreased 12% in the TKA leg ( P < 0.05) and tended to decrease (6%) in the contralateral leg ( P = 0.1). These data suggest cap-dependent translation initiation, and elongation may be inhibited during and after TKA surgery. We propose that cap-dependent translational events occurring during surgery may precipitate postoperative changes in muscle cells that contribute to the etiology of muscle atrophy following TKA.

Tourniquet Use During Knee Replacement Surgery May Contribute to Muscle Atrophy in Older Adults

“…mTORC1 inhibition by down regulation of Akt activates autophagy and inhibits translation initiation. We have demonstrated that during and after TKA, Akt and 4E-BP1 are hypophosphorylated, indicating a down regulation of translation initiation (1, 14, 37). In addition to initiation, further regulation of translation occurs via proteins controlling elongation.…”

“…We have shown that eEF2 is phosphorylated during and after TKA. Assimilated, during TKA, three significant control points regulating protein synthesis are altered: Akt, 4E-BP1, and eEF2 (1, 14, 37). These data suggest that during TKA-induced IR injury muscle protein synthesis is down regulated by reducing translation initiation and elongation (Figure 4).…”

“…eIF2α phosphorylation also selectively stimulates the expression of ATF4 and growth and arrest and DNA damage 34 (GADD34). We have measured an increase in eIF2α phosphorylation during TKA (14) as well as increases in ATF4 and GADD34 proteins (37). Each of these proteins (ATF4 and GADD34) is up regulated by eIF2α activity in response to skeletal muscle cell stress.…”

Essential amino acid supplementation in patients following total knee arthroplasty

“…The details on muscle volume determination have been published previously, with slight modifications for the current trial (56). Two weeks before surgery, patients had an MRI of the bilateral lower extremities between the anterior superior iliac spine and the tibial plateau at the Slocum Center for Orthopedics and Sports Medicine MRI facility equipped with a Philips Achieva 8C 1.5T system.…”

“…The total tourniquet time was recorded for each subject. All subjects also had three muscle biopsies performed at baseline (prior to tourniquet inflation), during maximal ischemia, and during reperfusion from the vastus lateralis muscle of the operated leg (results not reported here) (56,60,61).…”